This invention relates to a rear roof frame of motor vehicles.
In conventional mass-produced motor vehicles, in particular in “station wagons”, the rear roof frame comprises a multiplicity of individual sheet-metal pressed parts which are joined to form an inner shell and an outer shell which are joined, in particular welded, to form a hollow profile, with a hollow space being formed. The supporting device for the tailgate, which is fastened to the roof frame and can be pivoted upwards, is formed by hinges which are each fastened at one end to the rear roof frame. In addition, the tailgate is also supported by gas-filled springs which are coupled, on the one hand, to the rear post of the bodywork and, on the other hand, which are directly coupled to the tailgate. In order to ensure that the bodywork is leak proof, particularly in the corner region in the transition of the rear roof frame into the lateral roof frame which is open to the rear in the unfinished state, the shells have to be sealed to the outside in the flange regions in a complex and careful manner. This frequently requires environmentally incompatible sealants. Furthermore, the multipart nature and the welding connections which are affected by distortion give rise to tolerance problems which may also hinder the possibility of providing seal of the connection of the rear roof frame to the lateral roof frame and may have the consequence of the roof frame being complicated to align.
The open design of the rear roof frame in the corner regions toward the lateral roof frame means that the stiffness in the torsional and flexural direction is reduced, which may lead, in the driving mode and when opening the tailgate, to the frame becoming distorted, or else, after the motor vehicle has been used for a relatively long time, to damage due to sink marks on the frame. In order to counteract this, a multiplicity of additionally fitted stiffening plates may be fitted in the corner regions of the rear roof frame so as to ensure long-term operation of the vehicle, which results in an increased outlay on assembly and to an increased weight.
The invention is based on the object of providing a rear roof frame of a motor vehicle having a tailgate which is fastened to the roof frame, the roof frame, in spite of a shell-type construction, providing, in a simple manner and lightweight construction, sufficient torsional and flexural stiffness in order to withstand high mechanical stresses.
Owing to the invention, a complicated shell structure having stiffening plates is rendered superfluous, since the shell-type construction is limited just to two shells, an upper shell and a lower shell. Owing to the fact that, in the transition region of the rear roof frame to the lateral roof frame in the shell structure, hollow profiles having a knee-shaped section are arranged on both sides and are fastened to the structure, the rear roof frame obtains exceptional flexural and torsional stiffness transversely and longitudinally to the direction of the vehicle. The stiffness is particularly concentrated at the point at which the hinge of the tailgate is provided, with the result that, in the roof frame design according to the invention, the frame is not damaged during frequent pivoting actuation of the tailgate and other mechanical stresses of the vehicle during the driving mode which, inter alia, also have an effect on the rear roof frame in the form of distortions. Hollow profiles are simple to produce and are of low weight owing to their high stiffness characteristics in comparison to other conventionally stiffening sheet-metal constructions of shell-type constructions given comparable stiffness values. Owing to the tight linkage of the lateral roof frame to the rear roof frame in the form of a hollow profile which forms the end of the rear frame, an optimum introduction and distribution of force in the entire roof frame is obtained, this linkage making a further substantial contribution to stiffening the rear roof frame. The central part of the rear roof frame, which does not require special stiffening, remains flexurally slack in comparison to the remaining roof frame.
Owing to the fact that the end region of the rear and of the lateral roof frame, which is partially open to the rear in the unfinished state and is therefore weakened in terms of stiffness, is formed by hollow profiles, in particular by a single-piece, circumferentially closed hollow profile in the transition to the lateral roof frame, the weakening is overcompensated in a simple manner, this being of considerable advantage particularly during a side impact and if the motor vehicle overturns, because of the energy-absorbing effect. Welding flanges are no longer absolutely necessary for the production and are no longer of any significance when considering the leakproofness. The absence of gaps and welding flanges means that the hollow profile according to the invention does not allow any sealing problems to occur, it being possible for manufacturing to take place with substantially smaller tolerances than in a multipart shell construction. In view of its very high stiffness, the wall thickness can be reduced with an insignificant reduction in the stiffness, which saves structural space and weight. In an advantageous manner with respect to a space-saving and protected possibility of accommodating it, the hollow profile forms a receiving housing in which the hinge and/or the gas-filled compression spring is/are fitted. The hollow profiles may be designed as a blank, for example as a two-shell structure. As an alternative, extruded profiles or drawn tubes are conceivable. The hollow profiles may likewise be cut from a billet and welded along the longitudinal seam after a subsequent bending or rolling operation.
Furthermore, the multiplicity of parts for producing the rear roof frame and therefore the entire roof frame is reduced, which means that production and installation are not very complicated and that the production costs are reduced.